Synchronized Fireflies: Lighting Up Congaree

Make time between now and mid-June for one of the world’s most impressive lightning bug displays at South Carolina’s Congaree National Park

byBrent Crane

May 17, 2017

photo: Thomas Hammond

Love is in the air this weekend in South Carolina’s Congaree National Park, the 26,000-plus acres of old-growth bottomland forest outside of Columbia. Specifically, firefly (aka lightning bug) love. In one of the rarest springtime displays on earth, the local population of fireflies will begin blinking in rhythmic, repeated unison, known as a firefly synchrony event. The courtship displays occur in only about a dozen known spots around the globe, and “are spectacular,” says Jonathan Copeland, an emeritus professor of biology at Georgia Southern University and noted firefly expert. “It is like take-your-breath-away wow,” he says.

In the South, Tennessee’s Great Smoky Mountains National Park has long been a popular spot to witness the phenomenon, which occurs from around mid-May to mid-June. In Congaree, however, there are few crowds, no tickets, no required bus transportation. Just walk along the forest boardwalk and wait for the lights to come on. The nightly group-flickering lasts for about two to three weeks, starting just after sunset and stretching more than two hours. Another difference at Congaree: the species of firefly on display is the Photinus frontalis, not the Photinus carolinus that frequent the Smokies. Whereas the latter flashes intermittently, the bugs at Congaree perform a continuous flash “every second or so,” Copeland says.

photo: National Park Service

Congaree National Park.

Why the synchronized show? It works better for attracting females on the forest floor than a random onslaught of blinks, explains Andrew Moiseff, a University of Connecticut biologist who has co-published research on firefly synchrony with Copeland. In what is called “flash dialogue,” females respond to specific blink patterns with specific blinks of their own, calling down individual males from above.

Timed to the phenomenon, Congaree’s Harry Hampton Visitor Center will stay open until 9 p.m. from May 20 to June 10, with park rangers and volunteers on hand. For the best shot at catching a big show rather than a trickle, Moiseff recommends showing up around a week after the flashes begin, so as to ensure that you’ll catch the bugs “when they’re really spectacular.” In this case, Memorial Day Weekend. As of Tuesday, May 16, Congaree rangers have already reported seeing small amounts of synchronizing fireflies.

photo: Frederick Austin

Fireflies light up Congaree National Park.

Another tip: If photographing fireflies, forget the flash. The competition confuses them and, anyway, they’re notoriously difficult to capture on film. Unless you’re a well-equipped pro, save Instagram for another time. Better just to watch and enjoy the show.